1. Technical Field
The present invention relates generally to semiconductor design technology, and more particularly, to an anti-fuse circuit.
2. Related Art
When any one failed unit cell among numerous unit cells of a semiconductor memory apparatus is detected during a fabrication process, the semiconductor memory apparatus may not function as intended, and thus is discarded as a defective product. However, it is inefficient to discard the entire semiconductor memory apparatus as a defective product when failures occurred only in some unit cells thereof. Therefore, the semiconductor memory apparatus may be restored by replacing the failed unit cells with redundancy cells prepared therein, which makes it possible to improve the yield.
A repair operation using redundancy cells may be performed at a wafer level and a package level. At the wafer level, a fuse is used to perform the repair operation. For example, the repair operation using a fuse may include a method of cutting a fuse existing on a line connected to a row or column having a failed cell by applying an overcurrent, a method of burning a fuse using laser beams, a method of connecting junctions using laser beams, and a method of programming a fuse through EPROM.
The repair operation using a fuse may not be performed at the package level however. Therefore, an anti-fuse is used to perform a repair operation. The anti-fuse is a resistive fuse element having an electrical characteristic opposite to the fuse. In general, the anti-fuse may be formed of a thin dielectric material, such as a complex, in which a dielectric such as SiO2, silicon nitride, tantalum oxide, or ONO (silicon dioxide-silicon nitride-silicon dioxide) is interposed between two conductors. The anti-fuse is electrically open in a normal state. However, when a high voltage is applied to break down the dielectric between the conductors, the anti-fuse is shorted. When a failed cell is to be replaced at the package level, a programming operation for applying a high voltage to an anti-fuse circuit is performed. After the programming operation, the anti-fuse is shorted to thereby replace the failed cell with a redundancy cell.
In addition, the anti-fuse circuit may support various test modes depending on whether or not an anti-fuse is programmed. Accordingly, the anti-fuse circuit may be used in various ways inside a semiconductor apparatus.
However, the conventional anti-fuse circuit has a problem in that the anti-fuse sensitively reacts to external environments. When an external voltage level applied to the anti-fuse circuit unexpectedly rises, the anti-fuse may break down even though a program operation was not performed. In this case, a false fuse signal is generated and causes a malfunction of the entire semiconductor apparatus.